This invention relates to a position detector and, more particularly, to a position detector in which a movement of a permanent magnet is detected by a magnetic sensor element as a change in magnetic flux.
FIGS. 3 and 4 illustrate a related position detector in sectional view and circuit diagram, respectively. In these figures, the position detector comprises a magnetic sensor element 1 which includes a pair of magnetoresistance elements 1a and 1b made of NiFe ferromagnetic magnetoresistive material formed in a magnetoresistive pattern on a glass substrate. The magnetoresistance elements 1a and 1b are molded in a substantially rectangular insulating resin so that a magnetic sensing surface is formed by the magnetoresistance elements 1a and 1b on the glass substrate surface.
Reference numeral 2 designates a position detector mold case made for example of a polybuthyleneterephthalate resin, 3 is a rotary shaft rotatably mounted to the case 2, and 4 is an arm secured to one end of the rotary shaft.
Reference numeral 5 is a cylindrical permanent magnet secured to the other end of the rotary shaft 3, and 6 is a ceramic substrate serving as a circuit board on which a sensor circuit including a wiring pattern and various electronic components are mounted, the magnetic sensor element 1 being mounted on the ceramic circuit board 6 with its magnetic sensing surface placed in parallel to the substrate surface. Reference numeral 7 designates a terminal for taking out an output from the magnetic sensor element 1.
The ceramic circuit board 6 is inserted within the case 2 with its board surface perpendicular to the permanent magnet 5 or, that is, with the magnetic field from the permanent magnet 5 passing in parallel across the magnetic sensing surface of the magnetic sensor element 1.
Reference numeral 10 designates a Wheatstone bridge composed of the magnetoresistance elements 1a and 1b and reference voltage setting resistors R1 and R2, 11 is a temperature-compensated constant current circuit, 12 is a differential amplifier circuit, 13 is a level shift circuit and 14 is an output terminal of the level shift circuit 13.
When the position detector is applied to a throttle valve (not shown) of an internal combustion engine (not shown), the arm 4 is rotated in accordance with the opening degree of the throttle valve within an air-intake pipe of a vehicular engine, the rotation of the arm 4 is transmitted to the permanent magnet 5 through the rotary shaft 3. As the permanent magnet 5 rotates, the direction of magnetic flux passing in parallel across the magnetic sensing surface of the magnetic sensor element 1 changes, in accordance with which the resistance of the magnetoresistance pattern of the magnetoresistance elements 1a and 1b changes.
Accordingly, as the resistance of the magnetoresistance elements 1a and 1b varies, the output voltage from the output terminal O1 of the Wheatstone bridge 10 varies. At this time, the resistance values of the resistors R1 and R2 do not vary and a constant reference voltage is provided from the output terminal O2.
The output voltages supplied from the output terminals O1 and O2 of the bridge 10 are supplied to the input terminals I2 and I1, respectively, of the differential amplifier 12 where they are amplified and a difference between the two output voltages is generated at the level shift circuit 13 and the difference signal is supplied from the output terminal 14. This output voltage which has an output voltage waveform corresponding to a rotational angle of the permanent magnet 5 is supplied to an external apparatus (not shown) through the terminal 7 to indicate the opening degree of the throttle valve.
FIG. 5 illustrates another sensor circuit for use in a different application in which a negative characteristic output voltage waveform is required. As seen from FIG. 5, the output terminals O1 and O2 of the Wheatstone bridge 10 are connected to the input terminals I1 and I2, respectively, of the differential amplifier 12 so that the output terminal 14 supplies an output voltage waveform B shown in FIG. 6 exhibiting opposite characteristic as compared to the waveform A of the sensor circuit shown in FIG. 4.
According to the above-described related position detector, in order to provide two kinds of position detectors having two opposite polarity output characteristics in accordance with the application, it has been necessary to prepare and store two kinds of ceramic circuit boards 6 on which different sensor circuits are formed. Therefore, the number of parts to be manufactured and administrated is increased.